Two main issues of automotive design today concern the improvement of driving safety and fuel consumption efficiency. Suboptimal tire pressure may have negative impact on both of these aspects: on the one hand, the contact surface of an incorrectly inflated tire with the street is changed, possibly causing a longer braking distance, worsened side stability and handling of the vehicle and even an increased heat generation between tire and street; on the other hand, the tire pressure directly influences the fuel consumption.
Therefore, tire pressure monitoring systems are increasingly integrated in the vehicle electronic in order to warn the vehicle driver of any significant deviation from normal tire pressure.
Tire pressure monitoring systems in general work either directly (i.e. with a tire pressure sensor) or indirectly (i.e. having no tire pressure sensor). Direct monitoring systems are usually very precise, but expensive due to the required additional measuring equipment. Indirect systems are cheaper, but it is naturally more difficult to obtain reliable and useful results.
Indirect tire pressure monitoring systems mostly use for their estimations signals from existing sensors measuring, for instance, the angular velocity of the wheels, which are used by antilock braking systems (ABS). Based on the angular velocity signals the systems may in particular calculate changes in the wheel radii or observe the spectrum of the angular velocity signals. From this, the system may deduce information about tire pressure derivations. A conventional indirect tire pressure monitoring system is described in U.S. Pat. No. 6,501,373 B2.